[SI-LIST] Re: Decoupling of Oscillator
- From: "Martin Euredjian" <martin@xxxxxxxxxxxxxx>
- To: <si-list@xxxxxxxxxxxxx>
- Date: Thu, 21 Nov 2002 09:36:36 -0800
From: Tegan Campbell
> I'm dealing with this problem now(recommendation from the vendor is to use
> beads on both Vdd and Vss) and I need to nail this spin.
Right, I asked because differing recommendations gave me concern. When I
asked the individual vendors for the reason for having (or not) the ground
bead (or resistor) I never really got any sort of conclusive or qualitative
answer.
My concern is that you risk elevating the ground reference within the
circuit on the output side of the filter, which would mean the possibility
of missed logic levels or really funky edges (sorry, loose terminology) ...
which could cause delays and all sorts of other issues, I guess.
And then this all goes back to more general decoupling discussions held
here. If the output side of the filter has enough capacitors to cover a
wide frequency and current-requirement range ... what does this mean in
terms of the effect of that ground bead? Since, presumably, all that bead
will see, will be a few KHz, at most.
My gut feeling is that if you don't have enough mid to high frequency
decoupling on the output of the filter, and your circuit operates in the
MHz~GHz region, a lot of high frequency current will be forced through the
beads (or resistor), which might lead to greater radiation, Vcc and ground
level problems. This is just conjecture, I'm not really sure.
===============================
Martin Euredjian
eCinema Systems, Inc.
voice: 661-305-9320
fax: 661-775-4876
martin@xxxxxxxxxxxxxx
www.ecinemasys.com
===============================
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